The present invention relates to a seal for a ball screw, which is mounted to both end portions of a ball screw nut to seal inside the nut and also relates to a ball screw provided with such seal.
FIG. 14 shows one example of a seal or seal device of such a ball screw, disclosed for example, in Publication of Japanese Patent Laid-open No. 2000-230619, in which a thin plate of a synthetic resin is formed in shape of ring and the inner peripheral edge thereof is formed to provide a sharp edge. The seal 1 has an inner peripheral edge which contacts an outer peripheral surface or screw groove (threads) of a screw shaft 2 to thereby prevent foreign material or substance such as dust or dirt from invading into a gap between the screw shaft 2 and the ball screw nut 3.
FIG. 15 shows another example of a seal or seal member of such a ball screw, disclosed for example, in Japanese Utility Model Publication No. HEI 5-43310, in which a plurality of thin seal plates 4, formed from the same material, are laminated and inner peripheral edge portions of the laminated thin seal plates 4 contact a screw shaft 7. In this example of the seal for the ball screw, the inner peripheral edge portions of the respective thin plate seals 4 contact an outer peripheral surface or screw groove (threads) of the screw shaft 7 to thereby prevent foreign material such as dust or dirt from invading into a gap between the screw shaft 7 and the ball screw nut 6.
In the structure of the seal for the ball screw in the former example of FIG. 14, it is possible to prevent foreign material such as dust or dirt from invading into a gap between the screw shaft 2 and the ball screw nut 3 from an outside thereof. It is, however, impossible to prevent lubricant adhering to the outer peripheral surface or screw groove of the screw shaft 2 from extruding outward from the inside of the nut 3 through the seal 1. As a result, it is difficult to well retain the lubricant inside the ball screw nut 3.
On the other hand, in the structure of the seal for the ball screw in the latter example of FIG. 15, it is possible to prevent foreign material such as dust or dirt from invading into the ball screw nut from an outside thereof by the laminated seal plates 4. It is, however, also impossible to prevent lubricant adhering to the outer peripheral surface or screw groove of the screw shaft 2 from extruding outward from the inside of the nut 3 through the seal 1. As a result, in both examples, it is difficult to retain the lubricant inside the ball screw nut 3.